For months, I have yearned for the day that my iPad and iPhone would be updated with iOS 4.2, giving them amazing printing and media streaming skills. But when I finally got it all loaded up, I came to realize that the OS only delivers on all promises if you spend a small fortune on a bunch of new stuff.

Look over the promo for the long-awaited iOS 4.2 firmware update: AirPrint! Print e-mail, or Web pages, or photos, straight from the iPad over Wi-Fi. "There’s no software to download, no drivers to install, and no cables to connect." Nope, but there is the matter of owning one of the compatible printers, a very small list of HP models, starting at around $70. I was dismayed to find out that the HP I currently use, barely a year old, didn't make the cut.

Then there's AirPlay! Stream your digital media around the house, to any TV or speaker set ... that happens to be connected to an Apple TV ($99) or AirPort Express ($99). I gotta say, testing it out, it was impressive. Due to poor Wi-Fi reception in my TV room, I had a little trouble streaming my movie to the Apple TV, but when I got it working, it looked great. And there's some kind of joy to be had in firing up Pandora and then streaming it out — in the background — to some sound system while working or playing in another app. It's just that it's joy that will cost you $99 or more.

Ironically, even the one feature that iOS 4.2 explicitly offers as "free" — the Find My iPhone service — requires you to own the newest hardware: The free option is only available on the iPad, the iPhone 4 and the latest generation of iPod Touch.

For iPhones, that is about the sum total of what iOS 4.2 brings to the table. Its 4.1 software gives you the oh-so-important multitasking, the folder-based app organization, the unified e-mail inbox, the social gaming — all of the things that the iPad has been deprived of all these months. On that note, iPad owners should of course leap to upgrade their iPads — I have done it, and it seems to run nice and smooth.

But for iPhone owners who desire neither a new printer nor an Apple TV, the only other key advantage might be custom text-message ringtones. That's totally hot for some people, and by "some people," I mean "teenage girls."

Catch up with Wilson on Twitter at @wjrothman. Sad but true: He actually loves discussing the pros and cons of updating firmware.